Blade locking device for conical broached discs



Nov. 24, 1964 A. L. REID ETAL BLADE LOCKING DEVICE FOR CONICAL BROACHED DISCS I Filed July 16, 1962 Attorney United States Patent 3,158,353 BLADE LOUKING DEVIQE FOR CGNICAL BROACHED DESCS Alexander L. Reid, Greenfield Paris, Quebec, and Trevor L. Salt, Beloeil, Quebec, Qanada, assignors to United Aircraft of Canada Limited, Longueuil, Quebec,

Canada Filed July 16, 1962, Ser. N 210,618 1 Gains. (Cl. 255-77) The present invention relates to improvements in the construction of gas turbine rotors and more particularly to improvements in the construction of the blade wheels in such constructions.

In the attachment of the turbine blades to the turbine blade discs a lmown practice is to have the outer rim of the disc machined to provide a plurality of grooves or slots extending axially across their peripheral surfaces and to provide each blade with a root section matching the slots. A conventional form for such slots and roots is the multiple dovetail or fir-tree configuration. In the manufacture of such blading arrangement particularly in the case where conical blade fixings are used, means are also usually provided to lock the blades in their disc slots in the axial direction, for example, tangs are sometimes utilized for this purpose. If such tangs are utilized care must be taken that they are of adequate strength to resist bending stresses and moreover their insertion requires extra machine operations.

The present invention aims to provide a system of locking conical blade fixings to a blade disc which is light and simple compared with any corresponding tang device since it only involves the use of simple pins and avoids the production of bending stresses associated with tangs. These pins are located at a position sutiiciently removed from the lower neck of the fir-tree grooves of the disc (disc stub) and are angled axially through the disc so that they enter one disc stub and exit through the adjacent stub passing under the blade root therebetween. The pins are placed radially relative to the disc stubs and blade roots whereby an adequate shear area of the pins is presented to each blade root to resist movement.

This arrangement permits the production and assembly of blade discs and blades utilizing the minimum material while meeting with required root stub strengths and angle of annulus based on the locking advantages in the angular positioning of the pin.

Having thus generally described the nature of the invention, particular reference will be made to the accompanying drawings showing by way of illustration a preferred embodiment thereof, and in which:

FIGURE 1 is a view of segment of a conical turbine disc assembly with one end shown in radial cross section to illustrate the assembly more clearly.

FIGURE 2 is a sectional view of the construction of FIGURE 1 along the line 22.

FIGURE 3 is a sectional view of the construction of FIGURE 1 along the line 3--3.

FIGURE 4 is a greatly enlarged detail view in cross section of a blade root and blade receiving slot to illustrate shear bearing relationship of a locking pin in accordance with the invention.

FIGURE 5 is an enlarged view in perspective elevation of a typical disc groove and blade root with the adjacent disc stub removed for clarity.

With particular reference to FIGURE 1 a segment of a conical bladed disc for a gas turbine rotor is shown as being provided with turbine blades 18. The outer periphery of the disc is machined (usually broached) so as to provide a series of multiple dovetail or fir-tree slots 14 with intervening disc stubs 16 and each blade 18 is provided with a correspondingly profiled blade root 2!). With this arrangement, as shown, the blades 18 are assembled in sequence to the rim of the disc 1! by the axial insertion of the blade roots 24 into the slots 14. Since the disc segment 10 shown is part of a conically tapered rotor the forces exerted by rotation exert considerable transaxial pressure against such blade fixings requiring some means of blade retention in this direction.

In accordance with the present invention, a series of holes 22 are bored in regularly spaced apart relationship about the periphery of the disc iti so as to pass angularly from the center of one disc stub 16 to the center of the next adjacent disc stub 16 as shown in FIGURE 2, and angularly grooving the lowest section 21 of the blade root 2tl.' Retaining pins 24 are inserted in the borings 22, as shown in FEGURE 5 for example, to complete the assembly. As is shown most clearly in the cross section of FIGURE 2, angular disposition of the pins 24 provides sufiicient shear bearing surface contact to the blade root section 21 while making it possible to maintain the width of the blade root portion 21 at a minimum which in turn permits the width of the disc stubs 16 to be sufficient to meet desired requirements in the construction illustrated against possible fracture at the critical point of juncture between blade root and disc rim where maximum stresses apply.

While the radial location of the borings 22 and pins 24 illustrated is such that only a minor segment of the pin 2a is in shear bearing relationship with the blade root portion 21, see FIGURE 4, it will be under stood that the borings 22 could be extended radially to provide a greater shear bearing, say up to and including the full diameter of the pin 24 if desired. In this case the base dimensions A of the disc stubs 16 would be increased beyond those shown to meet desired safety factors of strength between blade roots and disc stubs as is known. 'As will be appreciated, number and spacing of blades, dimensions and forces to be met would be considered in determining pin size and degree of penetration with respect to shear strength.

As will be obvious by reference to the preceding description and accompanying drawings, the arrangement of the invention is equally suited for application in the assembly of non-conical blade fixing wherein, while the problem of axial forces effecting blade attachment may not be as critical, still at times requires some shear bearing retention between blade roots and disc. I

An additional feature of the present arrangement is that the borings 22 will act as a turbine disc burst inhibitor as described in detail in United States Patent 2,965,355, issued December 20, 1960. In the rotor construction described in this patent, which is similar to the rotor construction described with respect to blade attachment, means in the form of borings are provided sub stantially along a circumferential line through the basesv of the blade receiving slots for weakening the holding effect of the disc stubs and defining the region of fracture of the stub or projection from the disc.

The present pin receiving borings 22 though angularly placed and for an entirely different purpose, will act subtantially in the same manner as described in the above mentioned patent'as a disc burst inhibitor.

We claim:

In a rotor construction of the type having a conical blade supporting disc provided with a plurality of integral projections on its periphery detiining betweensaid projections axially extending slots following the taper of and surfa comprising a retaining member passing diagonally,

axially and through said disc periphery from side to side from the base of one of said disc integral projections on one transaxial surface of said disc to the base of an adjacent one of said projections on the other transaxial surface of said disc, each or" said retaining members engaging a single blade and at least sufficient of the base of said blade rotor portion in the lower portion or" the blade slot to provide a retaining shear surface, each of said retaining members comprising a pin and each of said pins extending diagonally through said disc periphery from substantially the center of the base of one of said disc integral projection on the other side.

References Eited in the file of this patent UNITED STATES PATENTS Kuti J'nly 3, Bodine Oct. 1, Gerdan et a1. Feb. 18, Spaeth Dec. 20, Kress Mar. 21, Rowley May 15, Hull et al June 18,

FOREIGN PATENTS Germany Oct. 11, Great Britain of Great Britain Aug. 13, Sweden Feb. 8,

OTHER REFERENCES Colwell and Cummings: 10 Ways to Attach Blades, 20 In SAE Journal, pages 32, 33, February 1948. 

